Naturally Speaking: Ames Flood Mitigation Study

By Steve Lekwa

Thursday

Apr 25, 2013 at 8:32 AM

The April 10 public input meeting on the City of Ames’ Flood Mitigation Study was pretty well attended, not only by Ames citizens, but also by people from Story City and rural areas north of Ames. Those areas would be affected by some of the alternatives proposed for solving Ames’ flood problems. I found the report presented by the city’s consulting firm to be pretty thorough, but didn’t completely agree with all the assumptions made by the consultants.

A big problem was pointed out by a member of the public regarding one of the major assumptions that all the recommendations were based on: the official 100- and 500-year flood probabilities. The city’s floodplain development policies and the consultant’s report are based on those standards. It was pointed out that the National Oceanic and Atmospheric Administration (NOAA) very recently expressed concerns that the existing standards, based on long-term past weather and flood records, no longer accurately predict current flood probabilities. NOAA feels that the old 100- and 500-year flood event standards do not adequately take into account recent upward trends in storm severity, frequency and precipitation quantities. Therefore, policies and plans based on them are more likely to underestimate flood frequency and severity.

Benefit-cost ratios (BCRs) were developed for each alternative and strategy for addressing Ames’ ongoing problems with flooding. A BCR of greater than 1 assumes benefits would exceed costs; less than 1 means costs would exceed benefits. Some of the highest BCR-rated options unfortunately wouldn’t do very much to reduce flooding. Some of the worst could actually have a pretty big impact on flood severity, but only at a cost that far exceeded the benefits derived.

The Ames City Council asked the consultants to reevaluate an option called Floodplain Storage that, according to the consultants, had a BCR of 1.13. The consultants noted, however, that the option would not protect against even an old standard 500-year flood and that it had potentially major environmental impacts. Those impacts affected agricultural land, 66 archeological sites, five historic structures, ISU housing and 25 private residences. The proposed work would also negatively impact Ames’ new aquatic center and significant portions of Story County Conservation’s Skunk River Greenbelt complex (SRGB). It’s worth noting that the SRGB was created as the best alternative to flooding portions of the Skunk River Valley as part of the old Skunk River Reservoir. Floodplain storage would flood less than that proposal, but would still leave unsightly and biologically impoverished mud flats much like the upper end of Saylorville Reservoir has become when flood waters recede. Lastly, the project, as proposed, would require the acquisition of well over 700 acres of private land. It’s safe to assume that many of those home and land owners might not be willing to sell their property.

Other members of the public pointed out that the real problem that may be too late to solve is floodplain development policies that continue to encourage filling and development in flood-prone areas. These policies have left Ames with few viable alternatives. The alternatives that remain are projected to be very expensive at a time when federal and state aid for such work is not likely to be forthcoming.

The consultant’s report does suggest that a combination of things might still be done that could at least somewhat reduce flood impacts. It was clear, however, that without massive expense and unacceptable environmental impacts, portions of Ames are still going to flood and that as long as valuable development remains in the floodplain, damage will still be likely.

(Steve Lekwa is retired director of Story County Conservation. He lives in Nevada.)